1. Field of the Invention
The present invention relates to a multipolar circuit breaker having a synthetic resin mold insulative casing.
2. Description of the Background Art
A circuit breaker has switch contacts, a switch mechanism operating the switch contact, a tripping mechanism operating when overcurrent flows to separate the switch contact via the switch mechanism, an arc extinguisher and the like disposed within a synthetic resin mold insulative casing.
An example of a conventional circuit breaker is disclosed in Japanese Patent Laying-Open No. 63-119126. FIG. 23 is a sectional view of this circuit breaker, viewed from the side. In the casing formed of a synthetic resin mold insulative base 100 and a synthetic resin mold insulative cover 101 coupled to each other through a screw are provided a main circuit conductor including a stationary switch contact 102 also serving as a terminal base, a movable switch contact 103, a flexible conductor 104, a unit conductor 105 in a trip unit 109 that will be described afterwards, and a terminal base 106. Also, a switch mechanism 107 operating movable switch contact 103, a trip unit 109 operating when overcurrent flows to release the engagement of a latch mechanism 108 to separate movable switch contact 103 from stationary switch contact 102 via the switch mechanism, and an arc extinguisher 110 are provided in the casing.
In such a conventional circuit breaker, there is a limit in the strength and tightening force of the screw that couples the base and cover together. Arc gas of high pressure generated when the circuit breaker cuts off a great short-circuit current will form a gap at the abutting face between the base and cover. The arc gas blows out through this gap at the side of the circuit breaker. There was a problem that the breaking capacity could not be increased.
This conventional circuit breaker must have a robust overall casing since the arc gas will spread entirely within the casing. There was also the problem that the conventional circuit breaker was increased in size and cost since the trip unit must be accommodated in the casing.
An object of the present invention is to provide a multipolar circuit breaker of large breaking capacity without arc gas blowing out from the sidewall.
Another object of the present invention is to provide a compact and inexpensive multipolar circuit breaker.
According to an aspect of the present invention, a multipolar circuit breaker includes a switch contact, an arc extinguisher, an input terminal, an output terminal, and an overcurrent tripping device for each pole. The multipolar circuit breaker includes a switch mechanism to operate the switch contact, and a trip mechanism to separate the switch contact through the switch mechanism in the operation of the overcurrent tripping device, common to each pole. The multipolar circuit breaker includes an arc extinguisher casing having a ceiling portion, a bottom portion and a sidewall joining the ceiling portion and the bottom portion and formed in continuity so that no gap is generated by an outward internal pressure. The switch contact and an arc extinguisher for each pole are stored in a separated manner from the counterpart of a neighbor pole by a partition wall separating respective poles, located parallel to the sidewall of the arc extinguisher casing.
Since the ceiling portion, bottom portion and sidewall of the arc extinguisher casing are formed continuously, absent of an abutting portion, arc gas will not blow out from the side of the circuit breaker. The configuration of the above-mentioned portion of the arc extinguisher casing being formed so that no gap is generated by the internal pressure includes the case where the members are formed integrally in continuity by integralmolding as well as the case where members are overlapped on each other to avoid formation of an abutting portion. The latter case includes the layering of another sheet-like member from the inner side of the abutting portion to prevent gap generation. The separation by the partition wall will prevent the arc gas, when generated at one pole, from affecting the other poles. The arc extinguisher casing is preferably a synthetic resin mold insulator having a rectangular cross section.
In the multipolar circuit breaker of the present aspect, the portion of at least the ceiling portion, bottom portion and the sidewall of the arc extinguisher casing can be formed in one piece by integral-molding. Therefore, fabrication thereof is simple.
In the multipolar circuit breaker of the present aspect, the arc extinguisher casing includes an upper member having the ceiling portion and the portion of the sidewall located at the ceiling side formed in one piece by integral-molding, and a lower member having the bottom portion and the portion of the sidewall located at the bottom side formed in one piece by integral-molding. Also, the portion of the sidewall of the upper member can be overlapped with the portion of the sidewall of the lower member. The sidewall formed by two sidewalls is absent of an abutting portion. Therefore, arc gas will not blow out at the side of the circuit breaker.
In the multipolar circuit breaker of the present aspect, the switch mechanism can be provided on the outer surface of the arc extinguisher casing. Therefore, the robust arc extinguisher casing that must withstand arc gas can be limited to the size that can store the switch contact and the arc extinguisher.
The multipolar circuit breaker of the present invention includes a switch unit with a switch contact, an arc extinguisher, an arc extinguisher casing, and a switch mechanism; a trip unit having an overcurrent tripping device stored in a synthetic resin mold insulative trip unit casing; and a synthetic resin mold insulative cover enclosing the switch unit and the trip unit.
By such a structure, a circuit breaker can be fabricated easily by assembling a switch unit and an overcurrent trip unit individually and then coupling both units with each other. Therefore, in the case where there are compatible units of a plurality of types due to difference in the rated current or the like, exchange is allowed even after the two units have been coupled. Also, only the arc extinguisher casing requires strength to withstand the arc gas, and the trip unit casing and cover may be of lower strength. Furthermore, a molded component that can entirely accommodate the arc extinguisher casing, switch mechanism and the trip unit casing is not required, so that the entire dimension can be reduced.
In the multipolar circuit breaker of the present invention, the synthetic resin mold insulative cover includes a ceiling portion that is substantially rectangular when viewed in plan, and a sidewall extending from the four sides of the ceiling portion and being in close contact with the arc extinguisher casing and trip unit casing in parallel. By virtue of this structure, the coupling of the two units is enhanced by the cover.
In the multipolar circuit breaker of the present invention, any one of a convex portion and a concave portion that are both engageable with the other counterpart is formed at respective sidewalls of the arc extinguisher casing and trip unit casing, whereas the other engageable counterparts of the convex portion or the concave portion are formed at least one pair of sidewalls opposite to each other of the synthetic resin mold insulative cover. By this structure, a screw to attach the cover is not required.
In the multipolar circuit breaker of the present invention, the connection portion of the main circuit conductor included in the switch unit and the trip unit can include a screw that is screwed in from the back side of the circuit breaker. By this structure, the space to attach the screwing tool at the surface side of the coupling portion is dispensable. This provides a margin in the structure of the switch mechanism and the trip mechanism.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.